Method for calibrating an active antenna

Abstract

In the field of active phase-control antennas, a method is provided for calibrating the phase center of an active antenna including a plurality of sub-elements able to receive a useful signal emitted by a satellite, the calibration being defined as a function of the reception characteristics of a reference signal at the level of each sub-element, the reference signal being emitted by the same satellite on a frequency band substantially equal to the frequency band of the useful signal and whose theoretical reception characteristics are known.

The invention claimed is: 
     
       1. A method of calibration of a phase centre of an active antenna comprising a plurality of sub-elements able to receive a useful signal emitted by a satellite,
 wherein said calibration is defined as a function of a reception gain and a reception phase of a reference signal at a level of each sub-element, the reference signal being emitted by a same satellite on a frequency band substantially equal to a frequency band of the useful signal, and whose theoretical reception phase and amplitude are known. 
 
     
     
       2. The method according to  claim 1 , further comprising:
 acquiring values of the reference signal and those of the useful signal at the level of each of the sub-elements of a reception antenna, 
 measuring possible discrepancy in phase and gain between the values of an actually received reference signal and theoretical reception values of the reference signal, 
 evaluating an optimal distribution law to be applied to the values of the signals so as to take account of possible disturbances, 
 applying a possible new calculated distribution law to the sub-elements of the antenna. 
 
     
     
       3. The method according to  claim 2 , wherein the measuring step is carried out by a correlation scheme. 
     
     
       4. The method according to  claim 3 , wherein the values of the reference signal are modified by varying these values in time and/or in frequency and/or in power so as to find a shape of a signal which has the best correlation with the reference signal actually received. 
     
     
       5. The method according to  claim 2 , wherein the various steps of the method are carried out in a sequential manner in real time. 
     
     
       6. The method according to  claim 2 , further comprising a step of storing for a predefined time interval the values of the reference signal and those of the useful signal measured at the level of each of the sub-elements of the reception antenna so as to perform the steps of the method in a deferred manner. 
     
     
       7. Use of the method according to  claim 1  for the calibration of the phase centre of an active antenna for receiving MEOSAR signals, wherein the reference signal is a GNSS signal and the useful signal is a MEOSAR signal.